1. Field of the Invention
The present invention relates to a synchromesh unit for a transmission for locking a gear relatively rotatably supported on a rotation shaft to the rotation shaft via a sleeve adapted to move in axial directions.
2. Description of the Related Art
The synchromesh unit for a transmission is disclosed in JP-B-48-24096. In this synchromesh unit, a sleeve splined to a hub fixed to a rotation shaft of the transmission is moved in an axial direction so that a blocking ring is pressed radially inwardly by projecting portions of spline teeth formed internally or along the inner periphery of the sleeve via a synchro-spring to thereby bring a gear relatively rotatably supported on the rotation shaft into friction engagement with the blocking ring so as to rotate in a synchronized fashion. Thus, the spline teeth of the sleeve mesh with dog teeth of the blocking ring and those of the gear, so that the gear is locked to the rotation shaft.
In the synchromesh unit described in JP-B-48-24096, when the projecting portions formed on the spline teeth of the sleeve ride on and pass over the synchro-spring, a pressing force applied to the synchro-spring is lost momentarily and this generates a lag in synchronization due to drastic decrease in synchronizing load, resulting in a drawback that noise is generated when the spline teeth of the sleeve come into mesh engagement with the dog teeth of the gear.
To cope with this problem, as described in JP-B-47-24054, it is conceived that the projecting portion of the spline teeth of the sleeve are formed longer in an axial direction so that the pressing force continues to be applied to the synchrospring to thereby secure the synchronizing load for a long time, whereby the lag in synchronization can be prevented. In this construction, however, a strong synchronizing load remains between the sleeve and the gear momentarily the spline teeth of the sleeve are brought into mesh engagement with the dog teeth of the gear, and as a result of this, the relative rotation of the sleeve and the gear is restricted, which makes it difficult to align phases of the spline teeth and the dog teeth with each other, this causing a risk that the spline teeth cannot smoothly mesh with the dog teeth.
The present invention was made in view of these situations, and an object thereof is to provide a synchromesh unit for a transmission in which the spline teeth of the sleeve can smoothly mesh with the dog teeth of the gear.
With a view to attaining the aforesaid object, according to a first aspect of the invention, there is provided a synchromesh unit for a transmission comprising a gear having dog teeth in an outer periphery thereof and supported on a rotation shaft in such a manner as to rotate relative thereto, a hub locked to the rotation shaft, a sleeve axially slidably splined to the hub, a blocking ring having in an outer periphery thereof dog teeth adapted to mesh with spline teeth in an inner periphery of the sleeve and disposed between the hub and the gear in such a manner as to be brought into friction engagement with the gear, and a synchro-spring supported on an outer periphery of the blocking ring, wherein the blocking ring is pressed toward the gear with the synchro-spring by pressing the synchro-spring radially inwardly by projecting portions of the spline teeth in the inner periphery of the sleeve as the sleeve moves axially, and in a state in which the blocking ring is in friction engagement with the gear, the spline teeth in the inner periphery of the sleeve are caused to mesh with dog teeth of the blocking ring and the dog teeth of the gear, whereby the gear is locked to the rotation shaft, the synchromesh unit being characterized in that the projecting portions of the spline teeth of the sleeve each comprise a first inclined surface adapted to apply an axial load to the blocking ring via the synchro-spring as the sleeve moves axially and a second inclined surface adapted to release the axial load, whereby when the spline teeth in the inner periphery of the sleeve reach a position just before the spline teeth in the inner periphery of the sleeve mesh with the dog teeth of the gear after the spline teeth in the inner periphery of the sleeve mesh with the dog teeth of the blocking ring, the synchro-spring moves to ride on the second inclined surface.
According to the above construction, after the first inclined surfaces formed on the projecting portions of the spline teeth of the moving sleeve applies a load to the synchro-spring so as to synchronize the sleeve with the gear, when the spline teeth formed in the inner periphery of the sleeve mesh with the dog teeth formed in the outer periphery of the blocking ring while the spline teeth of the sleeve reach positions just before the spline teeth mesh with the dog teeth, the synchro-spring moves to ride on the second inclined surface to thereby gradually reduce the synchronizing load between the sleeve and the dog teeth of the gear. This avoids a risk that the synchronizing load is drastically removed immediately before the spline teeth of the sleeve mesh with the dog teeth of the gear, and therefore, an interference with smooth mesh engagement between the spline teeth and the dog teeth can be prevented which will result from the generation of a lag in synchronization between the sleeve and the gear. In addition, the residual excessive synchronizing load is eliminated momentarily the spline teeth of the sleeve mesh with the dog teeth of the gear, and therefore, a relative rotation between the sleeve and the gear is permitted to thereby absorb a lag in phase between the spline teeth and the dog teeth, thereby making it possible to provide a smooth mesh engagement between the spline teeth and the dog teeth.
According to a second aspect of the invention, there is provided a synchromesh unit for a transmission as set forth in the first aspect of the invention, wherein the projecting portions of the spline teeth of the sleeve each has a flat surface extending axially between the first inclined surface and the second inclined surface.
According to the above construction, the flat surfaces are formed between the first inclined surfaces and the second inclined surfaces on the projecting portions of the spline teeth, and therefore, a positive shift feeling can be obtained by the reaction force of the load applied to the synchro-spring by the flat surface in shifting gears, whereby the shift feeling can be improved.